This invention relates to a valve operating mechanism for internal combustion and like-valved engines.
It has for some time been realized that the requirements for engine valve timing in an internal combustion engine are variable depending upon the speed of the engine when optimum operation is desired. Thus in the use of the usual mechanically operated valve system, operated by means of a camshaft, selection is dependent upon the maximum engine power at high speed operation, minimum exhaust emissions at low speed part-load operation, or on some form of compromise between the two. Considerable research has been undertaken on this subject which have largely produced the conclusion that, ideally, full control over every parameter of valve movement is required; and these parameters need to be varied in response to the operating conditions of the engine at any particular time. As a result of this research, various modifications have been proposed for existing camshaft installations, and in different ways in dependence upon the particular objectives which have been considered in the particular research involved. Nevertheless, no modification has been found which is capable of providing a full optimum control of the valve operation over the whole of the operating conditions of the engine, and, as a result, any proposed system is effectively only a compromise.